Base station apparatus and radio communication method

ABSTRACT

A wireless communication apparatus capable of minimizing the degradation in separation characteristic of a code multiplexed response signal. In this apparatus, a control part ( 209 ) controls both a AC sequence to be used in a primary spreading in a spreading part ( 214 ) and a Walsh sequence to be used in a secondary spreading in a spreading part ( 217 ) so as to allow a very small circular shift interval of the ZC sequence to absorb the interference components remaining in the response signal; the spreading part ( 214 ) uses the ZC sequence set by the control part ( 209 ) to primary spread the response signal; and the spreading part ( 217 ) uses the Walsh sequence set by the control part ( 209 ) to secondary spread the response signal to which CP has been added.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus and areference signal generating method.

BACKGROUND ART

In mobile communication, ARQ (Automatic Repeat Request) is applied todownlink data from a radio communication base station apparatus(hereinafter abbreviated to “base station”) to radio communicationmobile station apparatuses (hereinafter abbreviated to “mobilestations”). That is, mobile stations feed back response signalsrepresenting error detection results of downlink data, to the basestation. Mobile stations perform a CRC (Cyclic Redundancy Check) ofdownlink data, and, if CRC=OK is found (i.e. if no error is found), feedback an ACK (ACKnowledgement), and, if CRC=NG is found (i.e. if error isfound), feed back a NACK (Negative ACKnowledgement), as a responsesignal to the base station. These response signals are transmitted tothe base station using uplink control channels such as a PUCCH (PhysicalUplink Control CHannel).

Also, the base station transmits control information for reportingresource allocation results of downlink data, to mobile stations. Thiscontrol information is transmitted to the mobile stations using downlinkcontrol channels such as L1/L2 CCHs (L1/L2 Control CHannels). Each L1/L2CCH occupies one or a plurality of CCEs (Control Channel Elements). Ifone L1/L2 CCH occupies a plurality of CCEs, the plurality of CCEsoccupied by the L1/L2 CCH are consecutive. Based on the number of CCEsrequired to carry control information, the base station allocates anarbitrary L1/L2 CCH among the plurality of L1/L2 CCHs to each mobilestation, maps the control information on the physical resourcescorresponding to the CCEs occupied by the L1/L2 CCH, and performstransmission.

Also, to efficiently use downlink communication resources, studies areunderway to associate CCEs with PUCCHs. According to this association,each mobile station can decide the PUCCH to use to transmit responsesignals from the mobile station, from the CCEs corresponding to physicalresources on which control information for the mobile station is mapped.

Also, as shown in FIG. 1, studies are underway to performcode-multiplexing by spreading a plurality of response signals from aplurality of mobile stations using ZC (Zadoff-Chu) sequences and Walshsequences (see Non-Patent Document 1). In FIG. 1, (W₀, W₁, W₂, W₃)represents a Walsh sequence with a sequence length of 4. As shown inFIG. 1, in a mobile station, first, a response signal of ACK or NACK issubject to first spreading to one symbol by a ZC sequence (with asequence length of 12) in the frequency domain. Next, the responsesignal subjected to first spreading is subject to an IFFT (Inverse FastFourier Transform) in association with W₀ to W₃. The response signalspread in the frequency domain by a ZC sequence with a sequence lengthof 12 is transformed to a ZC sequence with a sequence length of 12 bythis IFFT in the time domain. Then, the signal subjected to the IFFT issubject to second spreading using a Walsh sequence (with a sequencelength of 4). That is, one response signal is allocated to each of foursymbols S₀ to S₃. Similarly, response signals of other mobile stationsare spread using ZC sequences and Walsh sequences. Here, differentmobile stations use ZC sequences with different cyclic shift values inthe time domain, or different Walsh sequences. Here, the sequence lengthof ZC sequences in the time domain is 12, so that it is possible to usetwelve ZC sequences with cyclic shift values “0” to “11”, generated bycyclically shifting the same ZC sequence using the cyclic shift values“0” to “11”. Also, the sequence length of Walsh sequences is 4, so thatit is possible to use four different Walsh sequences. Therefore, in anideal communication environment, it is possible to code-multiplexmaximum forty-eight (12×4) response signals from mobile stations.

Here, there is no cross-correlation between ZC sequences with differentcyclic shift values generated from the same ZC sequence. Therefore, inan ideal communication environment, as shown in FIG. 2, a plurality ofresponse signals subjected to spreading and code-multiplexing by ZCsequences with different cyclic shift values (0 to 11), can be separatedin the time domain without inter-code interference, by correlationprocessing in the base station.

However, due to an influence of, for example, transmission timingdifference in mobile stations, multipath delayed waves and frequencyoffsets, a plurality of response signals from a plurality of mobilestations do not always arrive at a base station at the same time. Forexample, as shown in FIG. 3, if the transmission timing of a responsesignal spread by the ZC sequence with cyclic shift value “0” is delayedfrom the correct transmission timing, the correlation peak of the ZCsequence with cyclic shift value “0” may appear in the detection windowfor the ZC sequence with cyclic shift value “1.” Further, as shown inFIG. 4, if a response signal spread by the ZC sequence with cyclic shiftvalue “0” has a delay wave, an interference leakage due to the delayedwave may appear in the detection window for the ZC sequence with cyclicshift value “1.” Therefore, in these cases, the separation performancedegrades between a response signal spread by the ZC sequence with cyclicshift value “0” and a response signal spread by the ZC sequence withcyclic shift value “1.” That is, if ZC sequences, cyclic shift values ofwhich are adjacent, are used, the separation performance of responsesignals may degrade.

Therefore, up till now, if a plurality of response signals arecode-multiplexed by spreading using ZC sequences, a sufficient cyclicshift value difference (i.e. cyclic shift interval) is provided betweenthe ZC sequences, to an extent that does not cause inter-codeinterference between the ZC sequences. For example, when the differencebetween the cyclic shift values of ZC sequences is 4, only three ZCsequences with cyclic shift values “0,” “4,” and “8” amongst twelve ZCsequences with cyclic shift values “0” to “11,” are used for the firstspreading of response signals. Therefore, if Walsh sequences with asequence length of 4 are used for second spreading of response signals,it is possible to code-multiplex maximum twelve (3×4) response signalsfrom mobile stations.

Non-Patent Document 1: Multiplexing capability of CQIs and ACK/NACKsform different UEs(ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/TSGR1_(—)49/Docs/R1-072315.zip)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

As described above, if a Walsh sequence with a sequence length of 4,(W₀, W₁, W₂, W₃), is used for second spreading, one response signal isallocated to each of four symbols (S₀ to S₃). Therefore, a base stationthat receives response signals from mobile stations needs to despreadthe response signals over a time period of four-symbols. On the otherhand, if a mobile station moves fast, there is a high possibility thatthe channel conditions between the mobile station and the base stationchange during the above four-symbol time period. Therefore, when thereis a mobile station moving fast, orthogonality between Walsh sequencesthat are used for second spreading may collapse. That is, when there aremobile stations moving fast, inter-code interference is more likely tooccur between Walsh sequences than between ZC sequences, and, as aresult, the separation performance of response signals degrades.

By the way, when some of a plurality of mobile stations moves fast andthe rest of mobile stations are in a stationary state, the mobilestations in a stationary state, which are multiplexed with the mobilestations moving fast on the Walsh axis, are also influenced byinter-code interference.

It is therefore an object of the present invention to provide a radiocommunication apparatus and reference signal generating method that canminimize degradation of the separation performance of response signalsthat are code-multiplexed.

Means for Solving the Problem

The radio communication apparatus of the present invention employs aconfiguration having: a first spreading section that performs firstspreading of a response signal using one of a plurality of firstsequences that can be separated from each other because of differentcyclic shift values; and a second spreading section that performs secondspreading of the response signal subjected to the first spreading, usingone of a plurality of second sequences, and in which a differencebetween cyclic shift values of first sequences associated withdifferent, adjacent second sequences, is less than a difference betweencyclic shift values of first sequences associated with the same secondsequence.

Advantageous Effect of Invention

According to the present invention, it is possible to minimizedegradation of the separation performance of response signals that arecode-multiplexed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a spreading method of response signals(prior art);

FIG. 2 is a diagram showing correlation processing of response signalsspread by ZC sequences (in the case of an ideal communicationenvironment);

FIG. 3 is a diagram showing correlation processing of response signalsspread by ZC sequences (when there is a transmission timing difference);

FIG. 4 is a diagram showing correlation processing of response signalsspread by ZC sequences (when there is a delay wave);

FIG. 5 is a block diagram showing the configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 6 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 1 of the present invention;

FIG. 7 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 1 of the present invention(variation 1);

FIG. 8 is a diagram showing association between the first sequences,second sequences and PUCCHs according to Embodiment 1 of the presentinvention;

FIG. 9 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 1 of the present invention(variation 2);

FIG. 10 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 1 of the present invention(variation 3);

FIG. 11 illustrates Walsh sequences according to Embodiment 2 of thepresent invention;

FIG. 12 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 2 of the present invention;

FIG. 13 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 3 of the present invention(variation 1);

FIG. 14 is a diagram showing association between ZC sequences, Walshsequences and PUCCHs according to Embodiment 3 of the present invention(variation 2); and

FIG. 15 is a diagram showing a spreading method of a reference signal.

BEST MODE FOR CARRYING OUT INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 5 illustrates the configuration of base station 100 according tothe present embodiment, and FIG. 6 illustrates the configuration ofmobile station 200 according to the present embodiment.

Here, to avoid complicated explanation, FIG. 5 illustrates componentsassociated with transmission of downlink data and components associatedwith reception of uplink response signals to downlink data, which areclosely related to the present invention, and illustration andexplanation of the components associated with reception of uplink datawill be omitted. Similarly, FIG. 6 illustrates components associatedwith reception of downlink data and components associated withtransmission of uplink response signals to downlink data, which areclosely related to the present invention, and illustration andexplanation of the components associated with transmission of uplinkdata will be omitted.

Also, in the following explanation, a case will be described where ZCsequences are used for first spreading and Walsh sequences are used forsecond spreading. Here, for first spreading, it is equally possible touse sequences, which can be separated from each other because ofdifferent cyclic shift values, other than ZC sequences. Similarly, forsecond spreading, it is equally possible to use orthogonal sequencesother than Walsh sequences.

Further, in the following explanation, a case will be described where ZCsequences with a sequence length of 12 and Walsh sequences with asequence length of 4, (W₀, W₁, W₂, W₃), are used. However, the presentinvention is not limited to these sequence lengths.

Further, in the following explanation, twelve ZC sequences with cyclicshift values “0” to “11” will be referred to as “ZC #0” to “ZC #11,” andfour Walsh sequences of sequence numbers “0” to “3” will be referred toas “W #0” to “W #3.”

Further, a case will be assumed in the following explanation where L1/L2CCH #1 occupies CCE #1, L1/L2 CCH #2 occupies CCE #2, L1/L2 CCH #3occupies CCE #3, L1/L2 CCH #4 occupies CCE #4 and CCE #5, L1/L2 CCH #5occupies CCE #6 and CCE #7, L1/L2 CCH #6 occupies CCEs #8 to #11, and soon.

Further, in the following explanation, the CCE numbers and the PUCCHnumbers, which are defined by the cyclic shift values of ZC sequencesand Walsh sequence numbers, are associated therebetween on a one to onebasis. That is, CCE #1 is associated with PUCCH #1, CCE #2 is associatedwith PUCCH #2, CCE #3 is associated with PUCCH #3, and so on.

In base station 100 shown in FIG. 5, control information generatingsection 101 and mapping section 104 receive as input a resourceallocation result of downlink data.

Control information generating section 101 generates control informationto carry the resource allocation result, on a per mobile station basis,and outputs the control information to encoding section 102. Controlinformation, which is provided per mobile station, includes mobilestation ID information to indicate to which mobile station the controlinformation is directed. For example, control information includes, asmobile station ID information, a CRC masked by the ID number of themobile station, to which control information is reported. Controlinformation is encoded in encoding section 102, modulated in modulatingsection 103 and received as input in mapping section 104, on a permobile station basis. Further, control information generating section101 allocates an arbitrary L1/L2 CCH in a plurality of L1/L2 CCHs toeach mobile station, based on the number of CCE(s) required to reportthe control information, and outputs the CCE number corresponding to theallocated L1/L2 CCH to mapping section 104. For example, when the numberof CCE(s) required to report control information to mobile station #1 isone and therefore L1/L2 CCH #1 is allocated to mobile station #1,control information generating section 101 outputs CCE number #1 tomapping section 104. Also, when the number of CCE(s) required to reportcontrol information to mobile station #1 is four and therefore L1/L2 CCH#6 is allocated to mobile station #1, control information generatingsection 101 outputs CCE numbers #8 to #11, to mapping section 104.

On the other hand, encoding section 105 encodes transmission data foreach mobile station (i.e. downlink data) and outputs the encodedtransmission data to retransmission control section 106.

Upon initial transmission, retransmission control section 106 holds theencoded transmission data on a per mobile station basis and outputs thedata to modulating section 107. Retransmission control section 106 holdstransmission data until retransmission control section 106 receives asinput an ACK of each mobile station from deciding section 116. Further,upon receiving as input a NACK of each mobile station from decidingsection 116, that is, for retransmission, retransmission control section106 outputs the transmission data associated with that NACK tomodulating section 107.

Modulating section 107 modulates the encoded transmission data receivedas input from retransmission control section 106, and outputs the resultto mapping section 104.

For transmission of control information, mapping section 104 maps thecontrol information received as input from modulating section 103 on aphysical resource based on the CCE number received as input from controlinformation generating section 101, and outputs the result to IFFTsection 108. That is, mapping section 104 maps control information onthe subcarrier corresponding to the CCE number in a plurality ofsubcarriers comprised of an OFDM symbol, on a per mobile station basis.

On the other hand, for transmission of downlink data, mapping section104 maps the transmission data, which is provided on a per mobilestation basis, on a physical resource based on the resource allocationresult, and outputs the result to IFFT section 108. That is, based onthe resource allocation result, mapping section 104 maps transmissiondata on a subcarrier in a plurality of subcarriers comprised of an OFDMsymbol, on a per mobile station basis.

IFFT section 108 generates an OFDM symbol by performing an IFFT of aplurality of subcarriers on which control information or transmissiondata is mapped, and outputs the OFDM symbol to CP (Cyclic Prefix)attaching section 109.

CP attaching section 109 attaches the same signal as the signal at thetail end part of the OFDM symbol, to the head of the OFDM symbol as aCP.

Radio transmitting section 110 performs transmission processing such asD/A conversion, amplification and up-conversion on the OFDM symbol witha CP, and transmits the result from antenna 111 to mobile station 200(in FIG. 6).

On the other hand, radio receiving section 112 receives a responsesignal transmitted from mobile station 200, via antenna 111, andperforms receiving processing such as down-conversion and ND conversionon the response signal.

CP removing section 113 removes the CP attached to the response signalsubjected to receiving processing.

Despreading section 114 despreads the response signal by a Walshsequence that is used for second spreading in mobile station 200, andoutputs the despread response signal to correlation processing section115.

Correlation processing section 115 finds the correlation value betweenthe response signal received as input from dispreading section 114, thatis, the response signal spread by a ZC sequence, and the ZC sequencethat is used for first spreading in mobile station 200, and outputs thecorrelation value to deciding section 116.

Deciding section 116 detects a correlation peak on a per mobile stationbasis, using a detection window set per mobile station in the timedomain, thereby detecting a response signal on a per mobile stationbasis. For example, upon detecting a correlation peak in detectionwindow #1 for mobile station #1, deciding section 116 detects theresponse signal from mobile station #1. Then, deciding section 116decides whether the detected response signal is an ACK or NACK, andoutputs the ACK or NACK to retransmission control section 106 on a permobile station basis.

On the other hand, in mobile station 200 shown in FIG. 6, radioreceiving section 202 receives the OFDM symbol transmitted from basestation 100, via antenna 201, and performs receiving processing such asdown-conversion and ND conversion on the OFDM symbol.

CP removing section 203 removes the CP attached to the OFDM symbolsubjected to receiving processing.

FFT (Fast Fourier Transform) section 204 acquires control information ordownlink data mapped on a plurality of subcarriers by performing a FFTof the OFDM symbol, and outputs the control information or downlink datato extracting section 205.

For receiving the control information, extracting section 205 extractsthe control information from the plurality of subcarriers and outputs itto demodulating section 206. This control information is demodulated indemodulating section 206, decoded in decoding section 207 and receivedas input in deciding section 208.

On the other hand, for receiving downlink data, extracting section 205extracts the downlink data directed to the mobile station from theplurality of subcarriers, based on the resource allocation resultreceived as input from deciding section 208, and outputs the downlinkdata to demodulating section 210. This downlink data is demodulated indemodulating section 210, decoded in decoding section 211 and receivedas input in CRC section 212.

CRC section 212 performs an error detection of the decoded downlink datausing a CRC, generates an ACK in the case of CRC=OK (i.e. when no erroris found) and a NACK in the case of CRC=NG (i.e. when error is found),as a response signal, and outputs the generated response signal tomodulating section 213. Further, in the case of CRC=OK (i.e. when noerror is found), CRC section 212 outputs the decoded downlink data asreceived data.

Deciding section 208 performs a blind detection of whether or not thecontrol information received as input from decoding section 207 isdirected to the mobile station. For example, deciding section 208decides that, if CRC=OK is found (i.e. if no error is found) as a resultof demasking by the ID number of the mobile station, the controlinformation is directed to the mobile station. Further, deciding section208 outputs the control information directed to the mobile station, thatis, the resource allocation result of downlink data for the mobilestation, to extracting section 205. Further, deciding section 208decides a PUCCH to use to transmit a response signal from the mobilestation, from the CCE number corresponding to subcarriers on which thecontrol information directed to the mobile station is mapped, andoutputs the decision result (i.e. PUCCH number) to control section 209.For example, if control information is mapped on a subcarriercorresponding to CCE #1, deciding section 208 of mobile station 200allocated with above L1/L2 CCH #1 decides that PUCCH #1 associated withCCE #1 is the PUCCH for the mobile station. For example, if controlinformation is mapped on subcarriers corresponding to CCE #8 to CCE #11,deciding section 208 of mobile station 200 allocated with above L1/L2CCH #6 decides that PUCCH #8 associated with CCE #8, which is theminimum number among CCE #8 to CCE #11, is the PUCCH directed to themobile station.

Based on the PUCCH number received as input from deciding section 208,control section 209 controls the cyclic shift value of the ZC sequencethat is used for first spreading in spreading section 214 and the Walshsequence that is used for second spreading in spreading section 217.That is, control section 209 sets a ZC sequence, the cyclic shift valueof which is associated with the PUCCH number received as input fromdeciding section 208, in spreading section 214, and sets the Walshsequence associated with the PUCCH number received as input fromdeciding section 208, in spreading section 217. The sequence control incontrol section 209 will be described later in detail.

Modulating section 213 modulates the response signal received as inputfrom CRC section 212 and outputs the result to spreading section 214.

As shown in FIG. 1, spreading section 214 performs first spreading ofthe response signal by the ZC sequence set in control section 209, andoutputs the response signal subjected to first spreading to IFFT section215.

As shown in FIG. 1, IFFT section 215 performs an IFFT of the responsesignal subjected to first spreading, and outputs the response signalsubjected to an IFFT to CP attaching section 216.

CP attaching section 216 attaches the same signal as the tail end partof the response signal subjected to an IFFT, to the head of the responsesignal as a CP.

As shown in FIG. 1, spreading section 217 performs second spreading ofthe response signal with a CP by the Walsh sequence set in controlsection 209, and outputs the response signal subjected to secondspreading to radio transmitting section 218.

Radio transmitting section 218 performs transmission processing such asD/A conversion, amplification and up-conversion on the response signalsubjected to second spreading, and transmits the resulting signal fromantenna 201 to base station 100 (in FIG. 5).

According to the present embodiment, a response signal is subjected totwo-dimensional spreading, by first spreading using a ZC sequence andsecond spreading using a Walsh sequence. That is to say, the presentembodiment spreads a response signal on the cyclic shift axis and on theWalsh axis.

Next, sequence control in control section 209 (in FIG. 6) will beexplained in detail.

If ZC sequences are used for first spreading of a response signal, asdescribed above, a sufficient cyclic shift value difference (e.g. cyclicshift value difference of 4) is provided between the ZC sequences, to anextent that does not cause inter-code interference between the ZCsequences. Therefore, orthogonality between response signals subjectedto first spreading using ZC sequences, cyclic shift values of which aredifferent, is little likely to collapse. By contrast, as describedabove, when there is a mobile station moving fast, orthogonality betweenWalsh sequences used for second spreading is likely to collapse.

Therefore, the present embodiment controls ZC sequences and Walshsequences according to the association shown in FIG. 7, such thatinterference components remained in response signals subjected todespreading in despreading section 114 (in FIG. 5) are absorbed by aslight difference between the cyclic shift values of ZC sequences. Thatis, control section 209 controls the cyclic shift values of ZC sequencesthat are used for first spreading in spreading section 214 and Walshsequences that are used for second spreading in spreading section 217,according to the association shown in FIG. 7.

FIG. 7 associates PUCCH #1 with ZC #0 and W #0, PUCCH #2 with ZC #4 andW #0, PUCCH #3 with ZC #8 and W #0, PUCCH #4 with ZC #1 and W #1, PUCCH#5 with ZC #5 and W #1, PUCCH #6 with ZC #9 and W #1, PUCCH #7 with ZC#2 and W #2, PUCCH #8 with ZC #6 and W #2, PUCCH #9 with ZC #10 and W#2, PUCCH #10 with ZC #3 and W #3, PUCCH #11 with ZC #7 and W #3, andPUCCH #12 with ZC #11 and W #3.

Therefore, for example, upon receiving as input PUCCH number #1 fromdeciding section 208, control section 209 sets ZC #0 in spreadingsection 214 and W #0 in spreading section 217. Also, for example, uponreceiving as input PUCCH number #2 from deciding section 208, controlsection 209 sets ZC #4 in spreading section 214 and W #0 in spreadingsection 217. Also, for example, upon receiving as input PUCCH number #4from deciding section 208, control section 209 sets ZC #1 in spreadingsection 214 and W #1 in spreading section 217.

Here, in FIG. 7, ZC sequences for first spreading when using W #1 insecond spreading (i.e. ZC #1, ZC #5 and ZC #9) are acquired bycyclically shifting the ZC sequences for first spreading when using W #0in second spreading (i.e. ZC #0, ZC #4 and ZC #8) by one. Also, ZCsequences for first spreading when using W #2 in second spreading (i.e.ZC #2, ZC #6 and ZC #10) are acquired by cyclically shifting the ZCsequences for first spreading when using W #1 in second spreading (i.e.ZC #1, ZC #5 and ZC #9) by one. Also, ZC sequences for first spreadingwhen using W #3 in second spreading (i.e. ZC #3, ZC #7 and ZC #11) areacquired by cyclically shifting the ZC sequences for first spreadingwhen using W #2 in second spreading (i.e. ZC #2, ZC #6 and ZC #10) byone.

Also, in FIG. 7, the difference between the cyclic shift values of ZCsequences associated with different, adjacent Walsh sequences, is lessthan the difference between the cyclic shift values of ZC sequencesassociated with the same Walsh sequence. For example, while the cyclicshift value difference is 1 between ZC #0 associated with W #0 and ZC #1associated with W #1, the cyclic shift value difference is 4 between ZC#0 and ZC #4 associated with W #0.

Thus, in FIG. 7, ZC sequences are cyclically shifted by one every timethe Walsh sequence number increases by one. That is, in the presentembodiment, the minimum difference is 1 between the cyclic shift valuesof ZC sequences associated with adjacent Walsh sequences. In otherwords, in FIG. 7, adjacent Walsh sequences are associated with ZCsequences, cyclic shift values of which are different, and used fortwo-dimensional spreading for response signals. Therefore, even wheninter-code interference between Walsh sequences occurs due to thecollapse of orthogonality between the Walsh sequences, it is possible tosuppress inter-code interference by spreading using ZC sequences. Forexample, referring to FIG. 7, a response signal that is transmittedusing PUCCH #4 is subjected to two-dimensional spreading using ZC #1 andW #1, and a response signal that is transmitted using PUCCH #7 issubjected to two-dimensional spreading using ZC #2 and W #2. Therefore,even when inter-code interference between W #1 and W #2 occurs due tothe collapse of orthogonality between W #1 and W #2, it is possible tosuppress the inter-code interference by a slight difference between thecyclic shift values of ZC #1 and ZC #2.

On the other hand, in FIG. 7, like ZC #1 and ZC #2, ZC sequences, cyclicshift values of which are adjacent, that is, ZC sequences, between whichthe cyclic shift value difference is “1,” are used. By this means,orthogonality between ZC sequences may collapse, which causes inter-codeinterference between the ZC sequences. However, in FIG. 7, ZC sequences,between which a cyclic shift value difference is “1,” are associatedwith different Walsh sequences and used for two-dimensional spreading ofresponse signals. Therefore, even when inter-code interference betweenZC sequences occurs due to the collapse of orthogonality between the ZCsequences, it is possible to suppress inter-code interference byspreading using Walsh sequences. For example, referring to FIG. 7, aresponse signal that is transmitted using PUCCH #4 is subjected totwo-dimensional spreading using ZC #1 and W #1, and a response signalthat is transmitted using PUCCH #7 is subjected to two-dimensionalspreading using ZC #2 and W #2. Therefore, even when inter-codeinterference between ZC #1 and ZC #2 occurs, it is possible to suppressinter-code interference by the difference between the sequences of W #1and W #2.

Thus, the present embodiment absorbs the collapse of orthogonality onthe Walsh axis (i.e. inter-code interference between Walsh sequences),on the cyclic shift axis, and absorbs the collapse of orthogonality onthe cyclic shift axis (i.e. inter-code interference between ZCsequences), on the Walsh axis. In other words, the present embodimentcompensates inter-code interference between Walsh sequences caused bythe collapse of orthogonality between the Walsh sequences, by thespreading gain of ZC sequence, and compensates inter-code interferencebetween ZC sequences caused by the collapse of orthogonality between theZC sequences, by the spreading gain of Walsh sequence. Therefore,according to the present embodiment, it is possible to minimizedegradation of the separation performance of code-multiplexed responsesignals.

FIG. 8 generalizes the association shown in FIG. 7. That is, FIG. 8illustrates a case where signals are spread using a plurality of firstsequences that can be separated from each other because of differentcyclic shift values and a plurality of orthogonal second sequences. Thatis, according to FIG. 8, when the difference between the cyclic shiftvalues of a plurality of first sequences associated with the same secondsequence is “k,” the difference between the cyclic shift values of aplurality of first sequences associated with a plurality of adjacentsecond sequences is “Δ” (Δ<k). That is, in FIG. 8, the first sequencesare shifted by Δ every time the second sequence number increases by one.

Also, as described above, the present embodiment can compensateinter-code interference between Walsh sequences by the spreading gain ofZC sequence, and compensate inter-code interference between ZC sequencesby the spreading gain of Walsh sequence. Therefore, it is possible tomake the difference between the cyclic shift values of ZC sequencesassociated with the same Walsh sequence less than “4” in FIG. 7. FIG. 9illustrates a case where this difference is “2.” While twelve PUCCHs ofPUCCH #1 to PUCCH #12 are available in FIG. 7, twenty-four PUCCHs ofPUCCH #1 to PUCCH #24 are available in FIG. 9. In other words, whiletwelve code resources amongst forty-eight code resources are used inFIG. 7, twenty-four code resources amongst forty-eight coded resourcesare used in FIG. 9. That is, the present embodiment can increase theefficiency of use of limited code resources and maximize the efficiencyof use of code resources.

Also, if the association shown in FIG. 10 are used, it is equallypossible to produce the same effect as in the case of using theassociation shown in FIG. 9.

Embodiment 2

As shown in FIG. 11, when W #0 is (1, 1, 1, 1) and W #1 is (1, −1, 1,−1), the first two-chip units in W #0 and W #1 are orthogonal to eachother, and the second two-chip units are orthogonal to each other.Similarly, when W #2 is (1, 1, −1, −1) and W #3 is (1, −1, −1, 1), thefirst two-chip units in W #2 and W #3 are orthogonal to each other, andthe second two-chip units are orthogonal to each other. Therefore, ifthe change of channel condition is sufficiently small during two symboltime periods, inter-code interference do not occur between W #0 and W #1and inter-code interference do not occur between W #2 and W #3.Therefore, it is possible to separate a plurality of response signalssubjected to code-multiplexing by second spreading using W #0 and W #1,into the first two-chip units and the second two-chip units. Similarly,it is possible to separate a plurality of response signals subjected tocode multiplexing by second spreading using W #2 and W #3, into thefirst two-chip units and the second two-chip units.

Therefore, with the present embodiment, control section 209 controls thecyclic shift value of a ZC sequence that is used for first spreading inspreading section 214 and a Walsh sequence that is used for secondspreading in spreading section 217 according to the association shown inFIG. 12. In FIG. 12, the cyclic shift values of ZC sequences associatedwith W #0 and the cyclic shift values of ZC sequences associated with W#1 are the same in 0, 2, 4, 6, 8 and 10, and the cyclic shift values ofZC sequences associated with W #2 and the cyclic shift values of ZCsequences associated with W #3 are the same in 1, 3, 5, 7, 9 and 11.

Here, for example, to separate the response signal subjected to secondspreading by W #0 when W #0, W #1 and W #2 are used for second spreadingat the same time, the sum of S₀, S₁, S₂ and S₃ in FIG. 1 is calculated.By this means, it is possible to remove the response signal componentsspread by W #1 and W #2, from a received signal. However, if a mobilestation that uses W #1 and a mobile station that uses W #2 move fast,the difference by channel variation is remained in a separated responsesignal as inter-code interference.

That is, referring to W #1, S₀ and S₁ have different signs, andtherefore the response signal component spread by W #1 is removed byadding S₀ and S₁. But, inter-code interference of Δ#1 by channelvariation is remained in the separated response signal. If the channelvariation is linear, similarly, inter-code interference of Δ#1 isremained in the separated response signal between S₂ and S₃. Therefore,inter-code interference of 2×Δ#1 in total is remained in the separatedresponse signal.

On the other hand, referring to W #2, S₀ and S₁ have the same sign, andtherefore response signal components spread by W #2 are removed by thedifference between the signs of S₂ and S₃. In this case, inter-codeinterference of 4×Δ#2 in total is remained in the separated responsesignal.

That is, inter-code interference is reduced between a plurality ofresponse signals subjected to code-multiplexing using a plurality ofWalsh sequences between which the first two-chip units are orthogonal toeach other and the second two-chip units are orthogonal to each other.Therefore, the present embodiment uses different Walsh sequences withlittle inter-code interference (e.g. W #0 and W #1) in combination withZC sequences, cyclic shift values of which are the same, and usesdifferent Walsh sequences with significant inter-code interference (e.g.W #0 and W #2) in combination with ZC sequences, cyclic shift values ofwhich are different.

As described above, according to the present embodiment, by performingsecond spreading of response signals using Walsh sequences in whichparts of the sequences shorter than the sequence length are orthogonalto each other, it is possible to improve the robustness to fast movementof mobile stations.

Embodiment 3

In code multiplexing by first spreading using ZC sequences, that is, incode multiplexing on the cyclic shift axis, as described above, asufficient difference is provided between the cyclic shift values of ZCsequences, to an extent that does not cause inter-code interferencebetween the ZC sequences. Therefore, orthogonality between ZC sequencesis little likely to collapse. Also, even if there is a mobile stationthat moves fast, orthogonality between ZC sequences does not collapse.On the other hand, in code-multiplexing by second spreading using Walshsequences, that is, in code-multiplexing on the Walsh axis, as describedabove, orthogonality between Walsh sequences is likely to collapse whenthere is a mobile station that moves fast. Therefore, uponcode-multiplexing response signals by second spreading, it may bepreferable to increase the average multiplexing level on the cyclicshift axis where orthogonality is little likely to collapse, anddecrease the average multiplexing level on the Walsh axis whereorthogonality is likely to collapse. Also, it may be preferable toequalize (unify) the multiplexing level on the Walsh axis between ZCsequences, such that the multiplexing level on the Walsh axis is notextremely high only in the response signal subjected to first spreadingby a certain ZC sequence. That is, when a response signal is subject totwo-dimensional spreading on both the cyclic shift axis and the Walshaxis, it may be preferable to reduce the average multiplexing level onthe Walsh axis and equalize (unify) the multiplexing levels on the Walshaxis between ZC sequences.

That is, the present embodiment controls ZC sequences and Walshsequences based on the association shown in FIG. 13. That is, controlsection 209 controls the cyclic shift value of a ZC sequence that isused for first spreading in spreading section 214 and a Walsh sequencethat is used for second spreading in spreading section 217 based on theassociation shown in FIG. 13.

Here, in CCE #1 to CCE #12 associated with PUCCH #1 to PUCCH #12 shownin FIG. 13, probability P to use physical resources for response signals(i.e. physical resources for PUCCH) corresponding to the CCE numbers orthe priority level of CCEs decreases in order from CCE #1, CCE #2, . . ., CCE #11 and CCE #12. That is, when the CCE number increases, the aboveprobability P monotonically decreases. Therefore, the present embodimentassociates PUCCHs with ZC sequences and Walsh sequences, as shown inFIG. 13.

That is, referring to the first and second rows along the Walsh axis(i.e. W #0 and W #1) in FIG. 13, PUCCH #1 and PUCCH #6 are multiplexed,and PUCCH #2 and PUCCH #5 are multiplexed. Therefore, the sum of thePUCCH numbers of PUCCH #1 and PUCCH #6, “7,” is equal to the sum of thePUCCH numbers of PUCCH #2 and PUCCH #5, “7.” That is, on the Walsh axis,PUCCHs of low numbers and PUCCHs of high numbers are associated andallocated. The same applies to PUCCH #3, PUCCH #4, and PUCCH #7 to PUCCH#12. Further, the same applies to the third row (W #2) and fourth row (W#3) on the Walsh axis. That is, in FIG. 13, between adjacent ZCsequences, the sum of the PUCCH numbers (i.e. the sum of the CCEnumbers) of adjacent Walsh sequences is equal. Therefore, in FIG. 13,the average multiplexing levels on the Walsh axis are substantiallyequal (substantially uniform).

Also, to equalize (unify) the multiplexing level on the Walsh axisbetween ZC sequences when the difference between the cyclic shift valuesof ZC sequences associated with the same Walsh sequence is “2” (in FIG.9), it is preferable to control ZC sequences and Walsh sequences basedon the association shown in FIG. 14.

In CCE #1 to CCE #24 associated with PUCCH #1 to PUCCH #24 shown in FIG.14, probability P to use physical resources for response signalscorresponding to the CCE numbers or the priority level of CCEs decreasesin order from CCE #1, CCE #2, . . . , CCE #23 and CCE #24. That is, asdescribed above, when the CCE number increases, the above probability Pmonotonically decreases.

Referring to the first and third rows on the Walsh axis (i.e. W #0 and W#2) in FIG. 14, PUCCH #1 and PUCCH #18 are multiplexed, and PUCCH #2 andPUCCH #17 are multiplexed. Therefore, the sum of the PUCCH numbers ofPUCCH #1 and PUCCH #18, “19,” is equal to the sum of the PUCCH numbersof PUCCH #2 and PUCCH #17, “19.” Also, referring to the second andfourth rows along the Walsh axis (i.e. W #1 and W #3) in FIG. 14, PUCCH#12 and PUCCH #19 are multiplexed, and PUCCH #11 and PUCCH #20 aremultiplexed. Therefore, the sum of the PUCCH numbers of PUCCH #12 andPUCCH #19, “31,” is equal to the sum of the PUCCH numbers of PUCCH #11and PUCCH #20, “31”. That is, on the Walsh axis, PUCCHs of low numbersand PUCCHs of the high numbers are associated and allocated. The sameapplies to PUCCH #3 to PUCCH #10, PUCCH #13 to PUCCH #16 and PUCCH #21to PUCCH #24. That is, in FIG. 14, similar to FIG. 13, between adjacentZC sequences, the sum of the PUCCH numbers (i.e. the sum of the CCEnumbers) of adjacent Walsh sequences is equal. Therefore, in FIG. 14,similar to FIG. 13, the average multiplexing levels on the Walsh axisare substantially equal (substantially uniform).

Thus, the present embodiment associates PUCCHs (i.e., CCEs) withsequences that are used for two-dimensional spreading, based onprobability P to use physical resources for response signalscorresponding to the CCE numbers or the priority level of CCEs. By thismeans, the average multiplexing level on the Walsh axis, that is, theexpected values of the number of multiplexed PUCCHs on the Walsh axisare substantially equal (or substantially uniform). Thus, according tothe present embodiment, the multiplexing level on the Walsh axis is notextremely high only in a response signal subjected to first spreading bya certain ZC sequence, so that it is possible to minimize the influencewhen orthogonality between Walsh sequences collapses. Therefore,according to the present embodiment, it is possible to further suppressthe degradation of the separation performance of response signalssubjected to code-multiplexing by second spreading.

Embodiments of the present invention have been described above.

Also, FIG. 7, FIG. 9, FIG. 10, FIG. 12, FIG. 13 and FIG. 14 illustrate acase of using four Walsh sequences of W #0 to W #3. But, in case ofusing two, three, five or more Walsh sequences, it is equally possibleto implement the present invention in the same way as above.

Also, the above embodiment shows a configuration to compensateinter-code interference between Walsh sequences by the spreading gain ofZC sequence. But, the present invention is applicable not only to caseswhere complete orthogonal sequences such as Walsh sequences are used forsecond spreading, but is also to cases where, for example, incompleteorthogonal sequences such as PN sequences are used for second spreading.In this case, inter-code interference due to the incompleteorthogonality of PN sequences is compensated by a spreading gain of ZCsequence. That is, the present invention is applicable to any radiocommunication apparatuses that use sequences, which can be separatedfrom each other because of different cyclic shift values, for firstspreading and sequences, which can be separated because of differencesof sequences, for second spreading.

Also, a case has been described above with the embodiments where aplurality of response signals from a plurality of mobile stations arecode-multiplexed. But, it is equally possible to implement the presentinvention even when a plurality of reference signals (e.g. pilotsignals) from a plurality of mobile stations are code-multiplexed. Asshown in FIG. 15, when three symbols of reference signals R₀, R₁ and R₂,are generated from a ZC sequence (with a sequence length of 12), first,the ZC sequence is subjected to an IFFT in association with orthogonalsequences (F₀, F₁, F₂) with a sequence length of 3. By this IFFT, it ispossible to acquire a ZC sequence with a sequence length of 12 in thetime domain. Then, the signal subjected to an IFFT is spread usingorthogonal sequences (F₀, F₁, F₂). That is, one reference signal (i.e.ZC sequence) is allocated to three symbols R₀, R₁ and R₂. Similarly,other mobile stations allocate one reference signal (i.e. ZC sequence)to three symbols R₀, R₁ and R₂. Here, individual mobile stations use ZCsequences, cyclic shift values of which are different in the timedomain, or different orthogonal sequences. Here, the sequence length ofZC sequences in the time domain is 12, so that it is possible to usetwelve ZC sequences with cyclic shift values “0” to “11,” generated fromthe same ZC sequence. Also, the sequence length of orthogonal sequencesis 3, so that it is possible to use three different orthogonalsequences. Therefore, in an ideal communication environment, it ispossible to code-multiplex maximum thirty-six (12×3) reference signalsfrom mobile stations.

Also, a PUCCH used in the above-described embodiments is a channel tofeed back an ACK or NACK, and therefore may be referred to as an“ACK/NACK channel.”

Also, a mobile station may be referred to as “UE,” a base station may bereferred to as “Node B,” and a subcarrier may be referred to as a“tone.” Also, a CP may be referred to as a “GI (Guard Interval).”

Also, the method of detecting an error is not limited to a CRC.

Also, a method of performing transformation between the frequency domainand the time domain is not limited to IFFT and FFT.

Also, a case has been described with the above-described embodimentswhere the present invention is applied to mobile stations. But, thepresent invention is also applicable to a fixed radio communicationterminal apparatus in a stationary state and a radio communication relaystation apparatus that performs the same operations with a base stationas a mobile station. That is, the present invention is applicable to allradio communication apparatuses.

Although a case has been described with the above embodiments as anexample where the present invention is implemented with hardware, thepresent invention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosures of Japanese Patent Application No.2007-159580, filed onJun. 15, 2007, and Japanese Patent Application No.2007-161966, filed onJun. 19, 2007, including the specifications, drawings and abstracts, areincorporated herein by reference in their entireties.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

1. A base station apparatus comprising: a transmitting sectionconfigured to transmit data to a mobile station apparatus and transmit,to the mobile station apparatus, control information related to the dataon a control channel element (CCE); and a receiving section configuredto receive a reference signal sequence, which is defined by one ofplural cyclic shift values, the reference signal sequence being spreadwith an orthogonal sequence, which is one of plural orthogonal sequencesand with which the one of plural cyclic shift values is associated, andtransmitted from the mobile station apparatus, wherein the one of pluralcyclic shift values and the one of plural orthogonal sequences aredetermined from an index of a resource associated with a CCE number, anda different cyclic shift value is associated with each of two of theplural orthogonal sequences.
 2. The base station apparatus according toclaim 1, wherein the index of a resource is associated one-to-one withthe CCE number.
 3. The base station apparatus according to claim 1,wherein the control information includes resource assignment informationof the data.
 4. The base station apparatus according to claim 1, whereinsaid transmitting section transmits the control information on one ormore CCE(s) with consecutive CCE number(s), and the resource isassociated with a first CCE number of the CCE(s) used for transmissionof the control information.
 5. The base station apparatus according toclaim 1, further comprising a despreading section configured to despreadthe received reference signal sequence.
 6. The base station apparatusaccording to claim 5, wherein said despreading section despreads withthe orthogonal sequence used for spreading the reference signalsequence.
 7. The base station apparatus according to claim 5, whereinsaid despreading section despreads with a different orthogonal sequencefor each of adjacent cyclic shift values of the plural cyclic shiftvalues.
 8. The base station apparatus according to claim 1, furthercomprising a correlation processing section configured to performcorrelation processing for the received reference signal sequence. 9.The base station apparatus according to claim 1, further comprising: adespreading section configured to despread the received reference signalsequence with the orthogonal sequence used for spreading the referencesignal sequence, and a correlation processing section configured toperform correlation processing for the despread reference signalsequence, wherein said despreading section despreads with a differentorthogonal sequence for each of adjacent cyclic shift values of theplural cyclic shift values.
 10. The base station apparatus according toclaim 1, wherein each of the plural orthogonal sequences is identifiedby a sequence index, and the sequence indices of the two of the pluralorthogonal sequences are different by one.
 11. The base stationapparatus according to claim 1, wherein the two of the plural orthogonalsequences are adjacent to each other.
 12. The base station apparatusaccording to claim 1, wherein each of adjacent cyclic shift values isassociated with a different orthogonal sequence.
 13. The base stationapparatus according to claim 1, wherein a minimum difference betweencyclic shift values that are respectively associated with the two of theplural orthogonal sequences is less than a minimum difference betweencyclic shift values that are associated with one of the pluralorthogonal sequences.
 14. The base station apparatus according to claim1, wherein each of the plural orthogonal sequences is identified by asequence index, and a cyclic shift value which is associated with eachof the plural orthogonal sequences is shifted by a predefined amount ofvalue for every increase by one in the sequence index.
 15. The basestation apparatus according to claim 1, wherein each of the pluralorthogonal sequences is identified by a sequence index, and a cyclicshift value which is associated with each of the plural orthogonalsequences is shifted by a predefined amount of value for every increaseby one in the sequence index, while an interval between cyclic shiftvalues which are associated with one of the plural orthogonal sequencesis constant.
 16. A radio communication method comprising: transmittingdata to a mobile station apparatus and transmitting, to the mobilestation apparatus, control information related to the data on a controlchannel element (CCE); and receiving a reference signal sequence, whichis defined by one of plural cyclic shift values, the reference signalsequence being spread with an orthogonal sequence, which is one ofplural orthogonal sequences and with which the one of plural cyclicshift values is associated, and transmitted from the mobile stationapparatus, wherein the one of plural cyclic shift values and the one ofplural orthogonal sequences are determined from an index of a resourceassociated with a CCE number, and a different cyclic shift value isassociated with each of two of the plural orthogonal sequences.